Many popular video compression standards, such as MPEG-1, MPEG-2 and H.263, are based on Discrete Cosine Transform (DCT). The basic approach of the DCT-based video compression technique is to subdivide the video image into non-overlapping blocks and then individually transform, quantize, and encode each block. However, using DCT-based compression techniques some artifacts may occur, especially at low and moderate bit rates. Two most noticeable artifacts are mosquito noise (or ringing artifact) and blocking artifact. Mosquito noise mostly appears in image homogeneous regions near strong edges. It is caused by loss of high frequency transform coefficients during quantization. Blocking artifacts appear as artificial discontinuities between the boundaries of the blocks. It is caused by independent processing of the individual blocks.
Many techniques have been proposed for removing mosquito noise and blocking artifacts. The basic steps for mosquito noise reduction usually include mosquito noise region detection and region adaptive filtering. The basic steps for blocking artifact reduction are to apply a low-pass filter across the block boundaries to smooth out the discontinuity. While various coding artifact reduction techniques have shown their effectiveness in different situations, a common shortcoming of such techniques is that they rarely consider the video quality of the input video. Therefore, such techniques treat the high quality video and the low quality video the same way, which unavoidably leads to over-smoothing of relatively high quality video, and insufficient artifact reduction for relatively low quality video.